Manual machine tool

ABSTRACT

The invention is based on a hand power tool, in particular a drill hammer and/or a chipping hammer, having a striking mechanism ( 14 ) capable of being driven in a housing ( 10 ) by an electric motor ( 12 ), via which an insertable tool ( 18 ) situated in a tool mount ( 16 ) is capable of being driven in an impacting manner, and having a sensor unit ( 30 ) via which a characteristic value for a no-load position can be detected. 
     It is proposed that, when a no-load position is detected via a motor control unit ( 22 ), the electric motor ( 12 ) and, therefore, the striking mechanism ( 14 ) can be actively decelerated.

BACKGROUND OF THE INVENTION

The invention is based generally on a hand power tool, in particular ahammer drill or rotary hammer.

A hand power tool is made known in EP 0 303 651 B2, a drill hammer, infact, having a striking mechanism capable of being driven by an electricmotor, in the case of which a clutch located in the drive traindisengages automatically when a specified quantity of motion detected bya sensor is reached, in fact, to interrupt a striking-driving actionbeing performed by the striking mechanism in a no-load position. Atravel position of a striking mechanism part or an insertable toollocated in a no-load path is detected as the quantity of motion. Whenthis travel position is left, the clutch automatically engages oncemore. When this travel position is reached, the sensor activates acontrol device that sends a control impulse to an electromagneticdisengage-control drive that grips the clutch and disengages it.

SUMMARY OF THE INVENTION

The invention is based on a hand power tool, in particular a drillhammer and/or a chipping hammer, having a striking mechanism capable ofbeing driven by an electric motor in a housing, via which an insertabletool situated in a tool mount is capable of being driven in an impactingmanner, and having a sensor unit, via which a characteristic value for ano-load position can be detected.

It is proposed that, when a no-load position is detected via a motorcontrol unit, the electric motor and, therefore, the striking mechanismcan be actively decelerated. An additional idle clutch and a safety stopfor a hammer can be avoided, and additional components, weight,installation space, installation expense, and costs can be spared.Problems with wear on an additional idle clutch can be prevented. Ashort no-load path can be achieved with a simple design and, as aresult, a short design of the hand power tool and low wear on the toolmount can be obtained.

Moreover, a high level of comfort can be achieved, particularly bycompletely eliminating an idle spring, e.g., by using a pressure sensorto determine a contact pressure of the insertable tool against an objectto be worked, or by designing an idle spring at least lightweight andwith a small positioning force, so that, advantageously, a smalloperating force is enough to reach a working position.

Advantageously, the striking mechanism can be designed exclusively interms of its impact function, and a no-load function can remainunconsidered. This results in design freedom. The striking mechanism canbe engineered to be robust by eliminating no-load holes and air vents,and an advantageous seal to prevent contamination and loss of lubricantcan be obtained.

A tailored and rapid run-up of the striking mechanism from the no-loadposition can be realized, and the transient behavior can be matched tothe striking mechanism using simple engineering by means of anappropriate operation of the electric motor. The means of attaining theobject, according to the invention, can basically be used with all handpower tools, the insertable tools of which are capable of being drivenin an impacting manner, as is the case, in particular, with impactdrills, drill hammers, chipping hammers, etc.

In principle, all electric motors appearing suitable to one skilled inthe art—such as asynchronous motors, synchronous motors, or DC devices,etc., for example—can be actively decelerated via a special motorcontrol unit, via a brake control. Particularly advantageously, theelectric motor is formed by an electronically commutated motor, however.Brushless, electronically commutated motors—reluctance motors, inparticular—are particularly overload-tolerant and can be loaded forshort durations with a high level of torque and, therefore, a high levelof braking torque. A high amount of current can flow without the risk ofbrush sparking.

Furthermore, an armature of the electronically commutated electric motorcan be designed having an overall smaller mass due to the absence of anarmature winding as compared with an armature of a conventional electricmotor having an armature winding. As a result, the armature of theelectronically commutated electric motor stores a small amount ofrotational energy during operation and can be decelerated rapidly usinglittle energy. The electronically commutated electric motor can beadvantageously decelerated with a large intermediate-circuit capacitoror with a brake chopper in a brake circuit.

If the striking mechanism is capable of being decelerated with aseparate brake unit, the active braking of the electric motor can besupported and a standstill of the electric motor and the strikingmechanism can be achieved particularly rapidly. The separate brake unitcan be designed in various ways, e.g., it can be formed by a mechanicalunit or an electromechanical unit, etc.

Particularly advantageously, a drive piston of the striking mechanism isdecelerated to a standstill between 0.1 to 3 impact strokes of thestriking mechanism after the no-load position is detected. This reduceswear on the striking mechanism and increases comfort, in particular bypreventing unnecessary vibrations.

If the striking mechanism comprises a pot-type piston, a cost-effectivepiston can be obtained, in the case of which a hammer and the piston arecapable of being interconnected by means of friction. Due to the directcontact between the pot-type piston and the hammer, the hammer can beaccelerated advantageously in a short time during transition from ano-load position to a working position via the pot-type piston and, withthe means of attaining the object according to the invention, it can beslowed in a short time during transition from a working position to ano-load position by means of the active deceleration of the electricmotor. In principle, however, the means of attaining the objectaccording to the invention can also be used with striking mechanismsthat comprise a piston guided in a cylinder or a hammer tube.

If a motor control unit is designed at least partially integral with analready-present power control unit of the electric motor, thencomponents, installation space, and weight can be advantageously spared.In the case of electronically commutated motors in particular, the motorcontrol unit can easily be designed integral with a power control unitof the electric motor.

The sensor unit can comprise various sensors appearing suitable to oneskilled in the art, e.g., electronic, electromechanical, and/ormechanical sensors, via which, however, it should be possible to detecta contact pressure of the insertable tool against an object to beworked, and/or a travel position of the insertable tool, or a componentmoved with the insertable tool, however. Particularly advantageously,the sensor unit comprises at least one electronic sensor. Saidelectronic sensor is small and easy to design and integrate—particularlyadvantageously—in space-saving fashion in small hand power tools. Theinformation from the sensor to the motor control unit can be transmittedvia electric lines, via radio, optically and/or mechanically, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages result from the following description of the drawing.An exemplary embodiment of the invention is shown in the drawing. Thedrawing, the description, and the claims contain numerous features incombination. One skilled in the art will advantageously consider themindividually as well and combine them into reasonable furthercombinations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a schematic representation of a partial cross-sectionthrough a drill hammer having a striking mechanism 14 capable of beingdriven in a housing 10 by an electric motor 12, whereby the electricmotor 12 is formed by an electrically commutated motor.

A pinion 36 is formed on an end of a shaft 34 of the electric motor 12facing an axis of rotation an insertable tool 18, which said pinionmeshes with a spur gear 40 supported on a bearing bolt 38. An eccentricpin 42 is fastened to the spur gear 40, via which a pot-type piston 24of the striking mechanism 14 can be driven. A hammer 26 is displaceablysupported in the pot-type piston 24, which said hammer acts via a punchdolly 46 on the insertable tool 18 secured in a tool mount 16 and on adrill bit secured in the tool mount 16.

Furthermore, the drill hammer comprises a sensor unit 30 having anelectronic sensor 20 via which a characteristic value for a no-loadposition can be detected.

According to the invention, when a no-load position is detected, theelectric motor 12 and, therefore, the striking mechanism 14, can beactively decelerated via a motor control unit 22, whereby the motorcontrol unit 22 is designed largely integral with an already-presentpower control unit 28 of the electric motor 12.

If the insertable tool 18 capable of being driven in an impacting mannerby the electric motor 12 via the eccentric pin 42, the pot-type piston24, the hammer 26, and the drill bit 46 is relieved by an object to beworked, a not-further-shown idle spring presses the drill bit 46—whichis actively interconnected with the insertable tool 18 and is axiallydisplaceably supported in the tool mount 16—axially into a home positionin the direction of the object to be worked. The electronic sensor 20 ofthe sensor unit 30 installed in the housing in the region of the toolmount 16 detects a no-load position or a travel position of the drillbit 46 associated with the no-load position and sends a signal via asignal line 32 to an evaluation unit 48 which, in turn, forwards a pulsevia a signal line 44 to the motor control unit 22.

The motor control unit 22 triggers an active braking of the electricmotor 12 in such a manner, in face, that electromagnetically generatedforces of the electric motor 12 act against the rotational direction ofthe shaft 34, and, after the no-load position is detected, the pot-typepiston 24 of the striking mechanism 14 comes to a standstill afterapproximately one impact stroke. The electric motor 12 also could bedecelerated by a separate braking unit 50, shown schematically FIG. 1.

If the insertable tool 18 is again pressed against an object to beworked and the drill bit 46 is pushed out of the no-load position intoits working position, the electronic sensor 20 sends a signal via thesignal line 32 to the evaluation unit 48 and this, in turn, sends asignal via the signal line 44 to the motor control unit 22, whichtriggers a tailored run-up of the electric motor 12 matched to thestriking mechanism 14 that is present.

Reference Numerals 10 Housing 12 Electric motor 14 Striking mechanism 16Tool mount 18 Insertable tool 20 Sensor 22 Motor control unit 24 Drivepiston 26 Hammer 28 Power control unit 30 Sensor unit 32 Signal line 34Shaft 36 Pinion 38 Bearing bolt 40 Spur gear 42 Eccentric pin 44 Signalline 46 Drill bit 48 Evaluation unit

1. A hand power tool, comprising: a striking mechanism (14) arranged ina housing (10) and with an electric motor (12), wherein the electricmotor (12) serves to drive the striking mechanism, wherein the strikingmechanism serves to drive an insertable tool (18) situated in a toolmount (16) in an impacting manner; and a sensor unit (30), wherein saidsensor unit serves to detect a characteristic value for a no-loadposition of the insertable tool; and an electric motor control unit(22), wherein the electric motor control unit serves to activelydecelerate the electric motor (12) and therefore the striking mechanism(14) when a no-load position is detected.
 2. The hand power toolaccording to claim 1, wherein the electric motor (12) is formed by abrushless, electronically commutated motor.
 3. The hand power toolaccording to claim 1, wherein a drive piston (24) of the strikingmechanism (14) is decelerated to a standstill after the no-load positionis detected between 0.1 and 3 impact strokes of the striking mechanism(14).
 4. The hand power tool according to claim 1, further comprising aseparate braking unit, wherein said separate braking unit serves todecelerate the striking mechanism (14).
 5. The hand power tool accordingto claim 1, wherein the striking mechanism (14) comprises a drive piston(24) formed by a pot-type piston.
 6. The hand power tool according toclaim 1, wherein the electric motor control unit (22) is designed atleast partially integral with an already-present power control unit (28)of the electric motor (12).
 7. The hand power tool according to claim 1,wherein the sensor unit (30) comprises at least one electronic sensor(20).
 8. The hand power tool according to claim 1, wherein the electricmotor control unit (22) controls the electric motor (12) upon activedeceleration in a manner such that electromagnetically produced forcesof the electric motor (12) act against a rotational direction of a shaft(34) of the electric motor (12).
 9. The hand power tool according toclaim 1, wherein the electric motor (12) has an armature without anarmature winding.
 10. The hand power tool according to claim 1, whereinthe hand power tool is a drill hammer.
 11. The hand power tool accordingto claim 1, wherein the hand power tool is a rotary hammer.